Recently, in the technical field of computer graphics including electronic games, rendering representation using a three-dimensional model is the mainstream. This is because the time needed for processing such as repetitive rendering or lighting calculation can be reduced when, for example, rendering frames at a plurality of continuous points of time while moving the same character or background like an animation. In particular, for an interactive content like an electronic game that changes the behavior of a rendering object in real time in correspondence with a dynamic factor such as an operation input, when a three-dimensional model or animation data is prepared in advance, it is possible to easily generate rendering representation from various viewpoint positions or view directions or rendering representation corresponding to a posture change of a rendering object. Such a three-dimensional graphics is normally rendered by constructing a three-dimensional model based on a plurality of two-dimensional images (cuts) prepared by a designer or the like and applying a texture to the model.
On the other hand, the three-dimensional graphics rendered by such texture application may give an impression different from the initial cut prepared by the designer or the like. Since the three-dimensional graphics basically “correctly” renders the three-dimensional model to which the texture is applied for a specific viewpoint, it is difficult to reproduce the representation of effective “presentation” in a specific view direction, like a cut rendered as a two-dimensional image. For this reason, even a game content or the like which places emphasis on the attraction of representation unique to a two-dimensional image and mainly uses two-dimensional images in a game screen holds a predetermined support.
However, particularly in a case in which a continuous change is presented like an animation, the method of performing predetermined rendering representation using two-dimensional images needs to prepare a two-dimensional image corresponding to the state of each frame for each change element (part or the like). Hence, the working amount of the designer or the like and the data amount of images necessary for the rendering representation of the elements can be large, as compared to the three-dimensional graphics. For example, in an animation that renders a target object at standstill while moving on the outer periphery of the object, frames in which the target object is rendered from various angles (view directions) are sequentially reproduced. In the three-dimensional graphics, rendering is performed by defining, for each frame, a camera that has a corresponding visual line direction and moves around a three-dimensional model concerning the object. In this case, necessary data are the three-dimensional model data of the target object and a texture applied to the model. On the other hand, when generating such an animation without using three-dimensional graphics, two-dimensional images corresponding to the view directions of frames need to be prepared. For an animation of, for example, 60 fps, it is necessary to simply prepare the data of 60 types of two-dimensional images.
NPL 1 discloses a method of generating an intermediate frame (so-called in-betweening frame) from discrete frames (key frames) by morphing to reduce the working amount of a designer.